Spectroscopic techniques that are sensitive to molecular chirality are important analytical tools to quantitatively determine enantiomeric excess and purity of chiral molecular samples. Many chiroptical processes however produce weak enantio-specific asymmetries due to their origin relying on weak magnetic dipole or electric quadrupole effects. Photoelectron circular dichroism (PECD) in contrast, is an intense effect, that is fully contained in the electric dipole description of light matter interaction and creates a chiral asymmetry in the photoelectron angular distribution. Here, we demonstrate that this chiral signature in the angular distribution of emitted electrons can be translated into the total photoemission yield for particulate matter. The resulting chiral asymmetry of the photoemission yield (CAPY), mediated by the attenuation of light within condensed particles, can be detected experimentally without requiring high vacuum systems and electron spectrometers. This effect can be exploited as an analytical tool with high sensitivity to chirality and enantiopurity for studies of chiral organic and hybrid submicron particles in environmental, biomedical or catalytic applications.

Spectroscopic techniques that are sensitive to molecular chirality are important analytical tools to quantitatively determine enantiomeric excess and purity of chiral molecular samples. Many chiroptical processes however produce weak enantio-specific asymmetries due to their origin relying on weak magnetic dipole or electric quadrupole effects. Photoelectron circular dichroism (PECD) in contrast, is an intense effect, that is fully contained in the electric dipole description of light matter interaction and creates a chiral asymmetry in the photoelectron angular distribution. Here, we demonstrate that this chiral signature in the angular distribution of emitted electrons can be translated into the total photoionization yield for submicron-sized condensed samples. The resulting chiral asymmetry of the photoionization yield (CAPY), mediated by the attenuation of light within the particles, can be detected experimentally without requiring high vacuum systems and electron spectrometers. This effect can be exploited as an analytical tool with high sensitivity to chirality and enantiopurity for studies of chiral organic and hybrid submicron particles in environmental, biomedical or catalytic applications.

Gold nanoparticles of various shapes were synthesized by reduction of gold salts in the presence of chitosan biomolecules as stabilizing agents. Fluorescence and photosensitizing properties of the rhodamine B dye were studied after its mixing with pure chitosan and chitosan-gold nanoparticle solutions. It was found that gold nanoparticles significantly affect the fluorescence intensity and the singlet oxygen production of the photosensitizer. Metal-enhanced fluorescence and metal-enhanced singlet oxygen generation effects were observed, probably as a direct consequence of the activation of the surface plasmon of the nanoparticles upon irradiation. Photosensitizing activity of the rhodamine B dye was investigated by using electron paramagnetic resonance (EPR) spectroscopy with TEMP as spin-trap molecules. The singlet oxygen generation was followed via changes in the intensity of EPR signal of the radical adduct, TEMPO. It was found that gold nanoparticles facilitate the production of singlet oxygen, while the chitosan molecules influence TEMPO stability and tend reduce the intensity of the EPR signal, especially at prolonged times following the irradiation.

Photothermal nanomotors driven by near-infrared (NIR) light emerged as a promising advancement in nanoscale propulsion systems. In this study, a novel type of nanomotor actuated by NIR light was prepared by decorating spherical TiO2 nanoparticles with Janus Ag-Ag2S nanoparticles. The motion of these nanomotors is studied using optical microscopy with a dual light source. It is found that they can be actuated with a 700 nm driving light and traverse significant distances relative to their size. Motion analysis reveals that their maximum velocity reaches similar to 20 mu m.s(-1), or about 100 diameters per second. Statistical analysis of over 400 nanomotor trajectories shows that around 60% of them move at maximum velocities of 6 to 12 mu m.s(-1). Vacuum ultraviolet velocity map imaging photoemission spectroscopy (VMI-PES) is conducted on isolated TiO2 and Janus Ag-Ag2S nanoparticles to elucidate electronic level alignment in the hybrid particle. The findings suggest that photothermal, rather than photocatalytic, effects drive nanomotor activation under NIR light. Additionally, our calculations indicate that the difference in absorption cross-sections between Ag-Ag2S and TiO2 components generates a temperature gradient (and consequently a pressure gradient) along the nanomotor, which in turn drives its motion. The local temperature rise near the nanomotors is a result of both photothermal effects within individual nanoparticles and thermal interactions between them.

Evaluating the biocompatibility of nanoparticles with blood is essential to demonstrate their biosafety, reduce potential adverse effects, and enable their application in nanomedicine. Although many studies have explored interactions between blood and nanomaterials, only limited number have specifically addressed the compatibility of nitrogen-doped carbon dots (N-CD) with red blood cells (RBC), the most abundant cells in blood, that are essential for healthy functioning of all vertebrates through their role in oxygen transport. This study investigated the biological properties of several concentrations (25, 50, 100, 200 μg/mL) of negatively charged, green fluorescent N-CD, synthesized using environmentally friendly precursors through a hydrothermal method, on healthy human RBC in vitro. Scanning electron microscopy and atomic force microscopy revealed that the treatment with N-CD, even at the highest concentration, did not significantly affect RBC morphology. Interfacial interaction between N-CD and RBC was demonstrated by photoluminescence spectroscopy, fluorescence microscopy, and synchronous fluorescence spectroscopy analysis. The treatment with N-CD at the highest concentration had no effects on the RBC osmotic fragility, slightly increased the RBC deformability, and demonstrated a noticeable protective effect on the RBC hemolysis after 24 h. Flow cytometry analysis confirmed that N-CD did not alter the RBC morphology and did not result in an increase in the production of reactive oxygen species or reactive nitrogen species, indicating that their interaction did not lead to oxidative stress induction in human RBC. These findings suggest that fluorescent N-CD are biocompatible, fluorescent RBC imaging agents and hold promise as candidates for developing novel RBC-based drug delivery systems.

Nitrogen-doped carbon dots (NCD) were synthesized using a simple and fast hydrothermal route, employing citric acid and urea as precursors. The resulting NCDs were non-covalently functionalized (conjugated) with aromatic amino acids, namely phenylalanine (Phe) and tryptophan (Trp). Atomic force microscopy revealed that the NCDs exhibit a disk-like morphology with an average diameter of approximately 60nm and an average height of about 0.5nm. Following conjugation, the particle height increased to around 3nm. UV-vis spectroscopy analysis indicated successful conjugation of the amino acids to the NCD nanostructures. Additionally, DFT numerical calculations based on three differently N-doped clusters were performed to elucidate the nature of the non-covalent interactions between NCDs and the corresponding amino acids. Photoluminescent spectra demonstrated a stable and strong fluorescence signal for both hybrids in the UV region. The most significant changes were observed in the case of Trp-conjugation. In contrast to phenylalanine, the non-covalent bonding of tryptophan to NCDs strongly influenced the visible emission (around 500nm) originating from surface states of the dots.

The valence band electronic structure of isolated silver iodide nanoparticles (AgI NP) was investigated by vacuum-ultraviolet aerosol photoelectron spectroscopy using the velocity map imaging technique (VUV VMI-PES). The VUV VMI-PES results were obtained for polydisperse aerosol produced by aggregation of hydrocolloid of silver iodide particles 8-15 nm in size. The ionization energy of the AgI particles was found to be 6.0±0.1 eV with respect to the vacuum level. The DFT calculations showed that the main contribution to the density of AgI electronic states in the valence region originates from I 5p orbitals. The dependence of the asymmetry parameter on the electron energy showed that the value of the characteristic energy loss of excited photoelectrons was 2.7 eV, which coincided with the band gap of the nanomaterial.

Gold nanoparticles were functionalized by amino acid tryptophan and vitamin riboflavin - a resonance energy transfer (RET) pair of biomolecules. The presence of the gold nanoparticles resulted in 65% increase in RET efficiency. Because of enhanced RET efficiency, the photobleaching dynamics of the fluorescent molecules at the surface of the nanoparticles is different from that of molecules in solution. The observed effect was used for detection of the functionalized nanoparticles within biological material rich with autofluorescent species. Synchrotron radiation deep-ultraviolet fluorescence microscopy is used to study the photobleaching dynamics of the fluorescence centers within human hepatocellular carcinoma Huh7.5.1 cells incubated with the nanoparticles. The fluorescent centers were classified according to their photobleaching dynamics, which enabled the discrimination of the cell areas where the accumulation of the nanoparticles takes place, even though the particles were smaller than the spatial resolution of the images.

Fluorescent nanocomposite films were prepared by solution mixing of polyvinyl alcohol (PVA) and tryptophan functionalized silver (AgTrp) nanoparticles. Synchrotron excitation deep-ultraviolet (DUV) fluorescence imaging was used to follow the distribution of AgTrp nanoparticles within the polymer matrix. Pronounced growth of dendrite-like structures in the presence of AgTrp nanoparticles was confirmed by bright field and fluorescence imaging as well as with atomic force microscopies. Both tryptophan and AgTrp nanoparticles influence thermal properties of the matrix. Differential scanning calorimetry measurements showed that they reduce crystallinity and significantly increase the glass transition temperature of PVA (in the case of PVA-AgTrp film the T-g increases by similar to 20 degrees C). Dielectric properties of the films were studied under two different conditions (dark and illumination). The illumination with 250 nm light induces a significant increase in conductance of the PVA-AgTrp nanocomposite. The relative changes, with respect to the conductance measured in the dark, were almost similar to 200%.

The angle-resolved photoelectron spectroscopy of isolated silver sulfide nanoparticles was carried out by using velocity map imaging technique at the DESIRS beamline of SOLEIL synchrotron facility. The reported spectroscopy results were obtained after interaction of the synchrotron radiation with a polydisperse aerosol produced from aqueous dispersion of silver sulfide particles, approximately 16 nm in diameter. The photoelectron and UV–Vis-NIR absorption spectra were used to estimate the maximum energy of the valance- and the minimum energy of the conduction-band of the nanoparticles. With respect to the vacuum level, the obtained values were found to be 5.5 ± 0.1 eV and 4.5 ± 0.1 eV for the valence band maximum and conduction band minimum, respectively. The dependence of the asymmetry parameter on the electron energy along the silver sulfide valence band showed an onset of inelastic scattering at ~ 1 eV electron kinetic energy.

Silver-bismuth iodide (Ag-Bi-I) rudorffites are chemically stable and non-toxic materials that can act as a possible lead-free replacement for methylammonium lead halides in optoelectronic applications. We report on a simple route for fabricating Ag-Bi-I colloidal nanoplatelets approximately 160 nm in lateral dimensions and 1-8 nm in thickness via exfoliation of Ag-Bi-I rudorffite powders in acetonitrile. The valence band electronic structure of isolated Ag-Bi-I nanoplatelets was investigated using synchrotron radiation to perform X-ray aerosol photoelectron spectroscopy (XAPS). The ionization energy of the material was found to be 6.1 +/- 0.2 eV with respect to the vacuum level. UV-vis absorption and photoluminescence spectroscopies of the Ag-Bi-I colloids showed that the optical properties of the nanoplatelets originate from I 5p to Bi 6p and I 5p to I 5p transitions, which is further confirmed by density functional theory (DFT) calculations. Finally, calculations based on the DFT and k . p theoretical methods showed that the quantum confinement effect is very weak in the system studied.

Structural changes at the molecular level, occurring at the onset of condensation, can be probed by angle-resolved valence photoelectron spectroscopy, which is inherently sensitive to the electronic structure. For larger condensed systems like aerosol particles, the observation of intrinsic angular anisotropies in photoemission (β parameters) is challenging due to the strong reduction of their magnitude by electron transport effects. Here, we use a less common, more sensitive observable in the form of the chiral asymmetry parameter to perform a comparative study of the VUV photoelectron spectroscopy and photoelectron circular dichroism (PECD) between pure gas phase enantiomers of the amino acid serine and their corresponding homochiral nanoparticles. We observe a relatively large (1%) and strongly kinetic energy-dependent asymmetry, discussed in terms of the emergence of local order and conformational changes potentially counterbalancing the loss of angular information due to electron transport scattering. This demonstrates the potential of PECD as a sensitive probe of the condensation effects from the gas phase to bulk-like chiral aerosol particles surpassing the potential of conventional photoemission observables such as β parameters.

Proline is a unique amino-acid, with a secondary amine fixed within a pyrrolidine ring providing specific structural properties to proline-rich biopolymers. Gas-phase proline possesses four main H-bond stabilized conformers differing by the ring puckering and carboxylic acid orientation. The latter defines two classes of conformation, whose large ionization energy difference allows a unique conformer-class tagging via electron spectroscopy. Photoelectron circular dichroism (PECD) is an intense chiroptical effect sensitive to molecular structures, hence theorized to be highly conformation-dependent. Here, we present experimental evidence of an intense and striking conformer-specific PECD, measured in the vacuum ultraviolet (VUV) photoionization of proline, as well as a conformer-dependent cation fragmentation behavior. This finding, combined with theoretical modeling, allows a refinement of the conformational landscape and energetic ordering, that proves inaccessible to current molecular electronic structure calculations. Additionally, astrochemical implications regarding a possible link of PECD to the origin of life’s homochirality are considered in terms of plausible temperature constraints.

This work reports on the selective on-line identification of polycyclic aromatic hydrocarbons (PAHs) formed in a low-pressure methane sooting flame, carried out using the double imaging Photoelectron Photoion Coincidence Spectroscopy method (i2PEPICO) on the DESIRS VUV beamline at the synchrotron SOLEIL. Generally, this work demonstrates the capabilities of the i2PEPICO method to identify PAHs in sooting flames, and in particular to distinguish cyclopentaring-fused PAHs (CP-PAHs) and side-substituted PAHs from their benzenoid isomers. Experimental threshold photoelectron spectra of four CP-PAHs: acenapthylene (C12H8, 152 m/z), acenaphtene (C12H10, 154 m/z), fluoranthene (C16H10, 202 m/z) and benzo(ghi)fluoranthene (C18H10, 226 m/z) are also reported for the first time.

We present an angle-resolved photoelectron spectroscopy study on isolated gold nanoparticles in the photon energy range between 6 and 12 eV performed at the DESIRS beamline of Synchrotron SOLEIL with a velocity map imaging spectrometer. The data are reported for polydisperse gold aerosols formed from hydrocolloids of bare and citrate-capped primary nanoparticles. The aerosols were brought to interact with the synchrotron radiation via a high-performance aerodynamic lens system developed for this study. The electronic structure of the aerosols was elucidated by threshold photoemission spectroscopy, which showed excellent agreement with the theoretical density of states. The photoionization cross sections of isolated gold particles were derived in the similar to 10(4) to 10(6) Mb range between 8 and 12 eV. We introduce a new methodology to extract all of the photoemission observables from the electron images as a function of electron energy, including photoelectron spectrum, anisotropy parameter b(2), and asymmetry parameter, alpha(E), which describes the shadowing asymmetry along the radiation propagation axis. The results show that electron energy distribution depends on the procedure used in the synthesis of the nanoparticles and on the ligand concentration. The dependence of the asymmetry parameter on electron energy along the valence band is rationalized through theoretical modeling in terms of the electric field distribution inside the particle and the losses due to inelastic scattering.

We report on the aerosol generation of ligand-free silver iodobismuthate (Ag-Bi-I) nanoparticles (NPs) and on in situ investigation of their electronic structure using synchrotron radiation soft X-ray aerosol photoelectron spectroscopy (XAPS). The structural and morphological characterizations revealed the aerosol to be composed of spherical rudorffite Ag3BiI6 particles, approximately 100 nm in size. The XAPS showed well-resolved signals from all expected elements (Ag, Bi, and I) and allowed estimation of the NP work function to be about 4.5 eV. The ionization energy of Ag3BiI6 NPs was determined to be 6.1 eV that is in good agreement with our calculations based on a hybrid functional approach. The presented method of production of Ag3BiI6 aerosol can prove beneficial for the future development of Ag-Bi-I-based photovoltaic materials, since it allows the deposition of Ag-Bi-I particles on large surface areas of arbitrary shape and roughness.

Titan, the largest moon of Saturn, is surrounded by a permanent thick photochemically-produced haze made of solid organic particles. These nanometer-sized particles spend about one year in suspension, undergoing further physical evolution during their atmospheric journey towards Titan's surface. In the present work we have simulated in the laboratory the emission of photoelectrons by submitting Titan's aerosols analogues to realistic EUV radiations. The aerosols are found to be easily ionized producing photoelectrons close to Titan's surface.

Interfacial charge transfer (ICT) complexes between wide-band-gap metal oxides and small colorless organic molecules have promising use in a variety of applications. The possibility to control optical properties and alignment of energy levels by a proper combination of inorganic and organic parts of ICT complexes is the main advantage of such materials. We used vacuum-ultraviolet electron imaging photoelectron spectroscopy (VUV PES) to determine the ionization potentials of isolated TiO2 nanoparticles surface-modified with salicylic acid (SA) and 5-aminosalicylic acid (5-ASA). The VUV PES measurements indicated a shift of the photoemission onset from 7.2 eV, observed for pristine TiO2 nanoparticles, to 6.5 and 5.9 eV for the surface-modified ones, with SA and 5-ASA, respectively. These results are consistent with the red shift of the absorption onset observed upon surface modification of TiO2 colloids. To obtain a detailed description of the optical properties of surface-modified TiO2 with SA and 5-ASA, density functional theory (DFT) calculations were performed with periodic boundary conditions (PBCs) and with a finite-size TiO2 cluster. The PBC model provides a qualitatively good description of electronic states of oxide surfaces functionalized with small organic molecules, while an excellent agreement between experimentally determined and calculated band gap values using a finite-size model was found.

Photoelectron circular dichroism (PECD) is an intense orbital-specific chiroptical effect observed as asymmetries in the angular distribution of photoelectrons produced by photoionization of randomly oriented pure enantiomers with circularly polarized light. After a broad introduction placing this effect in the context of new physical chiral-sensitive methods, we review the main characteristics of PECD in terms of molecular photoionization dynamics. We stress also the analytical capabilities of PECD to retrieve enantiomeric excesses (e.es.) and to probe subtle details of the whole molecular potential, some of them exemplified by the showcase camphor and fenchone molecules. We then present the case of the amino acid alanine for which an interplay between PECD and conformer population is rationalized. Based on this study, we propose a photophysical astrophysical scenario for the origin of life’s homochirality, relying upon the asymmetry of the associated recoiling alanine parent ion that could lead at the relevant Lyman-α energy to an e.e. of up to 4% in a given line of sight, which appears independent of the temperature. In an attempt to generalize this scenario to other amino acids, new data on proline showing an e.e. of 12%, of the same sign as alanine, are also presented. Abbreviations ARPES: Angle-resolved photoemission; CMS-Xa: Continuum multiple scattering with Xa local-exchange potential; CPL: Circularly polarized light; CD: Circular dichroism; CSM: Circumstellar medium; DPI: Dissociative ionization; HHG: High harmonics generation; HOMO: Highest occupied molecular orbital; ISM: Interstellar medium; KE: Kinetic energy; MS: Mass spectrometry; MW: Microwave; PAD: Photoelectron angular distribution; PECD: Photoelectron circular dichroism; PECD-PICO: Photoelectron circular dichroism / photoion coincidence; PEPICO: Photoelectron / photoion coincidence; PES: Photoelectron spectrum; PV: Parity Violation; REMPI: Resonance-enhanced multi-photon ionization; RH: Resistive heating; TD: Thermodesorption; UV: Ultra-violet; VMI: Velocity map imaging; VUV: Vacuum ultra-violet.